Comparing thermal performances of expressways constructed with an integral embankment and two separated embankments in permafrost zones

Linear transportation infrastructure constructed in permafrost zones is severely affected by permafrost degradation and the consequent thaw settlement. Considering the strong heat absorption of wide asphalt pavement, constructing an expressway with an integral embankment or two separated embankments in permafrost zones is under discussion at present. In this paper, thermal regime of permafrost beneath expressways constructed with an integral embankment (IE, 3 m in thickness) and two separated embankments (SEs, 3 m in thickness and with an 20 m wide separating strip) is investigated by numerical simulation with consideration of climate warming effect firstly. The results show that permafrost degradation beneath the IE is more significant than that beneath the SEs. Till the 50th operational year, the simulated permafrost table beneath the centerlines of the IE and the SEs decline by 6.5 m and 4.6 m, respectively, with a difference up to 1.9 m. The underlying permafrost warming beneath the IE is also severer than that beneath the SEs. Then, numerical simulations are carried out to investigate thermal regime and potential thermal interaction beneath the SEs with different widths of separating strip. The results show that when the separating strip is narrow than 20 m, thermal interaction between the SEs will lead to an asymmetric thermal regime beneath the two embankments. Compared with the outer side of the SEs, the permafrost table beneath the neighboring side of the SEs is deeper and the underlying permafrost is also warmer. Thermal interaction between the SEs can also lead to considerable permafrost degradation beneath the separating strip. Thus, the separating strip width should be considered during design of an expressway constructed with the SEs in permafrost zones.